DAVID Cameron stepped into an extraordinary row over the Duchess of Cambridge yesterday after Booker Prize-winning novelist Hilary Mantel labelled her a “shop-window mannequin” with a “plastic smile”.

Mantel created an uproar when she made scathing comments about the Duchess's media portrayal

The Prime Minister, on a trip to India, joined a host of politicians and celebrities who rallied to defend the honour of the future Queen.

Mantel, 60, author of award-winning Tudor historical novels such as Wolf Hall and Bring Up The Bodies, provoked outrage after making a controversial speech about the public’s relationships with the monarchy, reprinted this week in the London Review Of Books.

She described Kate, 31, as “a jointed doll on which certain rags were hung...a shop-window mannequin, with no personality of her own”.

Mantel said Kate “appeared to have been designed by committee and built by craftsmen, with a perfect plastic smile and the spindles of her limbs hand-turned and gloss-varnished.”

She compared her unfavourably to several prominent royal women from history, saying she lacked Princess Diana’s personality and was not a “power player” like Henry VIII’s second wife Anne Boleyn.

In her defence she said she was talking about the public’s perception and the media’s portrayal of Kate.

But it was too much for Mr Cameron, who led international condemnation of the remarks – even if he did mistakenly call the Duchess “Princess Kate”.

In a series of interviews, the Prime Minister attacked Mantel. “I think she writes great books,” he said, “but I think what she’s said about Kate Middleton is completely misguided and completely wrong.

“What I’ve seen of Princess Kate at public events, at the Olympics and elsewhere, is this, is someone who’s bright, who’s engaging, who’s a fantastic ambassador for Britain.

“We should be proud of that, rather than make these rather misguided remarks.”

“Kate Middleton is doing a brilliant job in a difficult role. She’s a huge asset to the country. She deserves our support in the roles that she’s playing.”

But the intervention of politicians did not go down well with everyone.

“When politicians air their views solely to garner some kind of public favour it’s totally nauseating,” wrote BBC Match Of The Day presenter Gary Lineker on the social media website Twitter.

Many big names followed Cameron's lead on Twitter and supported the PM's words

But I think what she’s said about Kate Middleton is completely misguided and completely wrong.

David Cameron

Mantel, who originally made the speech at the British Museum on February 4, refused to elaborate yesterday.

A man who answered the intercom at her seaside apartment in Budleigh Salteron, Devon, said the writer would not be making any further comment.

In the speech the double Booker Prize-winner said: “Kate seems to have been selected for her role of princess because she was irreproachable – as painfully thin as anyone could wish, without quirks, without oddities, without the risk of the emergence of character.

“She appears precision-made, machine-made, so different from Diana whose human awkwardness and emotional incontinence showed in her every gesture. Diana was capable of transforming herself from galumphing schoolgirl to ice queen, from wraith to Amazon.”

In a reference to Kate’s treatment for severe morning sickness as her pregnancy began, Ms Mantel goes on: “Once she gets over being sick, the press will find that she is radiant.

“They will find that this young woman’s life until now was nothing, her only point and purpose being to give birth.

“Presumably Kate was designed to breed in some manners,” she added, in a more widespread attack on the monarchy and the Queen, who gave her a CBE in 2006.

St James’s Palace declined to discuss the controversy but Claudia Joseph, author of Kate: The Making Of A Princess, said it was unfair to describe Kate as lacking in personality. Instead, she was someone who had learned to keep her feelings hidden and private.

“The reason William chose Kate is because she is discreet and doesn’t show her feelings in public,” she said. “That doesn’t mean she has no feelings.”

Nick Barton, chief executive of Action on Addiction, which counts Kate as its patron, said Mantel was entirely wrong to characterise her as a clothes horse whose only purpose is to give birth.

He said: “Having met the Duchess several times, I find her to be engaging, natural and genuinely interested. You can tell a lot about someone from the questions they ask and she asks really good questions, the questions of someone who wants to learn. She is also an intelligent woman.

“Having her as patron draws attention to the cause of addiction as a whole. She is doing an enormous amount to reduce the stigma of addiction and increase understanding of it.”